Field of the Invention
This invention relates generally to filament winding or wrapping and, more particularly, to filament winding or wrapping of inflator devices such as used in motor vehicle occupant safety restraint systems.
Discussion of Related Art
It is well known to protect a vehicle occupant by means of safety restraint systems which self-actuate from an undeployed to a deployed state without the need for intervention by the operator, i.e., “passive restraint systems.” Such systems commonly contain or include an inflatable vehicle occupant restraint or element, such as in the form of a cushion or bag, commonly referred to as an “airbag cushion.” In practice, such airbag cushions are typically designed to inflate or expand with gas when the vehicle encounters a sudden deceleration, such as in the event of a collision. Such airbag cushions may desirably deploy into one or more locations within the vehicle between the occupant and certain parts of the vehicle interior, such as the doors, steering wheel, instrument panel or the like, to prevent or avoid the occupant from forcibly striking such parts of the vehicle interior. For example, typical or customary vehicular airbag cushion installation locations have included in the steering wheel, in the dashboard on the passenger side of a car, along the roof line of a vehicle such as above a vehicle door, and in the vehicle seat such as in the case of a seat-mounted airbag cushion. Other airbag cushions such as in the form of knee bolsters and overhead airbags also operate to protect other or particular various parts of the body from collision.
In addition to one or more airbag cushions, inflatable passive restraint system installations also typically include a gas generator, also commonly referred to as an “inflator.” Upon actuation, such an inflator device desirably serves to provide an inflation fluid, typically in the form of a gas, used to inflate an associated airbag cushion. Various types or forms of inflator devices have been disclosed in the art for use in inflating an inflatable restraint system airbag cushion.
One particularly common type or form of inflator device used in inflatable passive restraint systems is commonly referred to as a pyrotechnic inflator. In such inflator devices, gas used in the inflation of an associated inflatable element is derived from the combustion of a pyrotechnic gas generating material.
Typically, pyrotechnic inflators include a pressure vessel housing so as to be able to withstand the 10 MPa to 30 MPa internal pressures created during combustion of the pyrotechnic gas generating material contained within the inflator. In practice, such pressure vessels are commonly made by welding together two or more metal, e.g., steel or aluminum, components after the loading therein of the inflator internal contents, such as the pyrotechnic gas generating material, for example.
Another particularly common type or form of inflator device used in inflatable passive restraint systems is commonly referred to as a compressed gas inflator. In such inflator devices, gas used in the inflation of an associated inflatable element is derived from stored compressed gas.
In conventional inflator devices of such type, the temperature and pressure within the gas storage chamber typically increases significantly during the initiation stage such as to provide an internal pressure sufficient to rupture a discharge end burst disk and permit gas flow from the storage chamber, through a diffuser and out to an associated inflatable airbag cushion. Thus, such inflator devices are commonly designed and constructed to have a sidewall of significant thickness to withstand the increase in internal pressure realized upon actuation of the inflator device. Unfortunately, increasing the thickness of the sidewall can result in inflator devices that are heavier and larger than desired.
Moreover, in reasonably long such pressure vessel housings having a cylindrical shape (e.g., where length is greater than diameter), the stress in the hoop direction is twice the stress in the axial direction.
Typically, compressed gas inflators include a pressure vessel housing designed so as to be able to withstand pressures in the range of 1.5 to 2 times the internal pressures created upon actuation of the compressed gas inflator, where such internal pressures are commonly at least 40 MPa up to 140 MPa, or more narrowly at least 55 MPa up to 120 MPa, or even more narrowly at least 65 MPa up to 110 MPa. In practice, such pressure vessels are typically elongated cylindrical in form and are made of steel of sufficient strength, i.e., thickness, to withstand the pressure within the vessel both during normal at-rest or pre-actuation state as well as upon actuation and functioning of the device. Moreover, desired system design and operation typically involves or includes the addition or incorporation of an appropriate safety factor to the expected actual pressures.
Automotive industry efforts directed towards inflatable restraint systems that are smaller, lighter, and less expensive to manufacture has led to the development of inflator assemblies such as disclosed in above-referenced U.S. Pat. No. 8,297,653 wherein an overwrap such as comprising a composite of fibers and a resin matrix system is applied over, on or about at least a portion of an inflator subassembly such as includes a metal housing of reduced thickness to form an inflator assembly that withstands the pressure generated therewithin upon actuation.
Commercially available filament winding machinery generally comprises a means for supporting and rotating a mandrel/part form, a means for supplying a continuous band of resin impregnated filamentary material, and a winding head which reciprocates along the length of the mandrel/part while moving both laterally and pivotally with respect to the mandrel/part for maintenance of proper filament orientation as the impregnated filament is wound around the mandrel/part form. Typically, two to six axes of movement are required to realize a desired wrap pattern, dependent on the complexity of the wrap pattern. For example, to wrap filament in the shape of “hoops” such as around a cylinder, i.e., such a wrap commonly referred to as a “hoop wrap,” a machine with two axis of movement could be used. However, to wrap filament around an object such as has been desired for various inflator devices such as used or incorporated in various motor vehicle occupant safety restraint systems a filament wrap in a generally helical form or pattern, i.e., such a wrap commonly referred to as a “helical wrap,” a machine or apparatus with at least four axis of rotation is typically required. For example, a first axis rotates the object along its longitudinal axis and must be turned at a variable rate depending on winding head position. A second axis moves the winding head laterally along the length of the part. A third axis moves the winding head toward the centerline of the part as the filament wraps around the ends. A fourth axis rotates the winding head to keep the filament flat on the part and prevents twists in the filament as it wraps around the end of the part when the winding head changes directions moving toward the other end of the part. A sophisticated computer program is required to synchronize the movement of all of the axes to properly place the filament and to prevent the winding head from accidently contacting the mandrel/part.
Furthermore, commercially available equipment is designed primarily for aerospace applications. As compared to motor vehicle occupant safety restraint systems such of specific interest herein, such commercial aerospace applications typically employ or are practiced on much larger parts, e.g., parts of significantly greater physical dimensions, and in much smaller production quantities. Moreover, such prior applications may have per part process times that amount to tens of minutes to even hours per part. In contrast, production processes for motor vehicle occupant safety restraint system components must typically run at processing times of no more that about 10 to 15 seconds per part in order to be commercially practical.
In view of the above, there is a need and a demand for a filament winding or wrapping apparatus and method that desirably simplifies the winding or wrapping process.
There is a need and a demand for a filament winding or wrapping apparatus and method that desirably reduces the complexity and/or sophistication of the controls or programming required to achieve the wrapping process.
There is a need and a demand for a filament winding or wrapping apparatus and method that desirably reduces the time period required to achieve a desired wind or wrap such as whereby mass production of filament wound or wrapped objects such as inflator devices such as used or incorporated in various motor vehicle occupant safety restraint systems can be realized.